1. Field of the Invention
The present invention relates to a laminated heat exchanger formed by laminating tube elements and fins alternately over a plurality of levels and which is used in the cooling cycle of an air conditioning system for vehicles.
2. Description of the Related Art
This type of laminated heat exchanger, which has been in development by this applicant, is formed by laminating tube elements alternately with fins over a plurality of levels. Each tube element has a pair of tank portions at one side and a U-shaped passage portion that communicates between the pair of tank portions. Also, in this type of laminated heat exchanger, tank groups that are provided parallel to each other along the direction of the lamination are formed by providing communication between the tank portions of adjacent tube elements and by providing partitions between the tank groups at specific positions thus a specific number of communicating areas are created. For instance, when forming communicating areas so that a heat exchanging medium flows through four passes relative to the airflow path of the laminated heat exchanger by partitioning one of the tank groups that are provided parallel to each other, two communicating areas A and B are formed in the tank group on one side and, in the other tank group, a communicating area C is formed, which communicates throughout without a partition. With this, a heat exchanging medium flow path extends from the communicating area A through the U-shaped passage portions to the tank group in the communicating area C which corresponds to the tank group in the communicating area A, and then extends from this tank group in the communicating area C to the tank group in the communicating area C that corresponds to the tank group in the communicating area B. Then, from the tank group in the communicating area C, it extends through the U-shaped passage portions to reach the communicating area B. In this case, if the intake and outlet portions for the heat exchanging medium are to be formed on one of the side surfaces of the heat exchanger, a communicating passage that connects an intake and outlet portion to a tank group located further away from the intake and outlet portions of the heat exchanging medium flow path mentioned earlier is required. In the prior art they are connected by a communicating pipe provided between a pair of tank groups that lie parallel to each other along the direction of lamination.
In addition, each of the tube elements is formed by bonding two formed plates, and in order to induce the heat exchanging medium into the U-shaped passage portion, a plurality (for instance, three) of shoal-like beads are formed in the area where the tank portion changes to the U-shaped passage portion. The shoal-like beads formed in each formed plate are bonded flush to each other to form heat exchanging medium guide channels.
To be more specific, as shown in FIG. 11, an enlarged tank portion 7a, to which the communicating passage is connected, is formed by extending a tank portion 7 into the space between the tank portions, and a connecting pipe 28, which functions as the communicating passage described earlier, is inserted into the enlarged tank portion 7a. With this, fluid that flows into the enlarged tank portion 7a from the communicating pipe 28 reaches the area that faces opposite the opening portion of the communicating pipe 28, where it changes direction by 90.degree., and then is induced into the adjacent tank portion 7, from which it flows into the U-shaped passage portion by travelling through the heat exchanging medium guide channels 37.
However, with the laminated heat exchanger structured as described above, it has been confirmed through rupture testing, in which a high pressure fluid (a fluid at 30-40 Kg/mm.sup.2) is made to flow inside, that a rupture occurs at the shoal-like bead 36c, closest to the connecting portion where the communicating passage (the communicating pipe 28) is connected. The main cause for this is that the tank wall portion facing opposite the opening portion of the communicating passage becomes distended by the pressure of the fluid sent from the communicating passage 28, as indicated with the broken line, and with this, the shoal-like bead 36c is subjected to a greater force than that applied to the other shoal-like beads 36a and 36b, which tends to break the bond.